1. Field of the Invention
The present invention relates to an improved ammunition having a body covered with a protective layer and to a method of making same.
2. Description of the prior Art
It is known to provide protective coatings for nitrocellulose ammunition cases.
For example in German published application No. 1 912 727 there is disclosed a porous, combustible casing made out of a swellable, expandable, natural or synthetic polymer or a derivative thereof which acts as a barrier. This barrier layer in turn, after its solidification, is provided with a moisture-proof, protective layer.
Published German application No. 1 578 062 discloses a combustible cartridge having no housing with a coating consisting of a highly combustible film, the film containing a mixture of dyes, pigments, or metal powder (for example aluminum or zinc). J. Brzuskiewicz in U.S. Pat. No. 3,987,731 discloses a porous combustible cartridge case containing nitrocellulose, reinforcing fibers and a resinous binder, which is rendered resistant to water and oil by coating the surface with a composite coating containing an undercoating of polyvinyl alcohol and a top coating of a copolymer of vinylidene chloride and acrylonitrile.
In general, there is the requirement regarding ammunition having a combustible cartridge casing that an uncontrolled premature ignition of the ammunition due to contact with hot substances or parts either inside the weapon or outside the weapon is prevented while simultaneously not preventing the combustion of the ammunition at a preselected time. Additionally, it is desired that the protective surface coating shall provide moisture resistance and waterproofing as well as protection against deterioration resulting from fungi or contaminating oil.
The afore-described properties of the protective surface coating and particularly the ease of combustibility providing complete combustion without residues and the simultaneous presence of flame retarding characteristics are not met satisfactorily in any of the prior art ammunition. For example, the protective coatings of the German published applications Nos. 1 912 727 and 1 578 062 have satisfactory moisture resistant and waterproofing characteristics, but they are flammable and therefore do not solve the safety problem attendant upon combustible cartridge casings and ammunition having no cartridge casings.
The ammunition described in U.S. Pat. No. 3,987,731 uses as a starting material fiber reinforced nitrocellulose employing in particular acrylic fibers and as a binder polyvinylacetate resin. Nitrocellulose having a nitrogen content of up to about 12.6 weight percent has the disadvantage of dissolving easily when contacted with a dissolving solution such as with a xylene solution. This nitrocellulose with relatively low nitrogen content has no oxidation reserve and therefore one has to expect the formation of residues upon firing. The acetate of the binder of U.S. Pat. No. 3,987,731 forms only a physical bond with the nitrocellulose material, is also susceptible to solvents, and there is a considerable transmission of such a casing.
According to U.S. Pat. No. 3,987,731 a first layer of polyvinyl alcohol primer lacquer is employed and then a layer of polyvinylidene chloride acrylonitrile copolymer lacquer. The first layer is insoluble in the solvents of the polyvinylidene chloride acrylonitrile copolymer lacquer and for obtaining the heat protective effect such a large amount of aluminum is combined with the polyvinylidene chloride acrylonitrile copolymer as to make combustion without a residue very doubtful. Furthermore, the combustion of the polyvinylidene chloride results in chlorine and/or hydrochloric acid and their derivatives which can increase erosion of the container of the cartridge. The weight of the layer amounts to more than 1.1 to 6 weight percent of the total weight of the ammunition. Such an amount is excessively high and constitutes a serious drawback. The large amount of material forming the coating is not burned without any residue during firing.
The protective coatings of the state of the art, for the reasons enumerated hereinabove, have not satisfactorily solved the opposed and contradictory requirements that are involved, i.e., no satisfactory compromise has been found between the necessary protective effect desired and the external influence of heat and the necessary requirement of complete combustion without residue during the firing of the shell.